1. Field of the Invention:
This invention relates to a method of brazing an aluminum material, i.e. aluminum or an alloy thereof, by forming a chemically coated flux layer on its surface and heating it.
2. Description of the Prior Art:
Brazing of an aluminum material is usually carried out by employing an Al-Si eutectic alloy having a melting point which is somewhat lower than that of the aluminum material. In order to enable the brazing alloy to combine satisfactorily with the aluminum material, it is necessary to remove any contaminant, such as an oxide film, from the surface of the aluminum material. A flux is applied to the surface of the material to remove any such contaminant therefrom.
The inventors of this invention found potassium pentafluoroaluminate (K.sub.2 AlF.sub.5) effective as a flux for brazing an aluminum material. A brazing method employing this flux forms the subject matter of Japanese Patent Application No. 191311/1983 corresponding to U.S. Application No. 659,423. It is characterized by forming a flux layer of K.sub.2 AlF.sub.5 on the surface of the aluminum material by chemical conversion coating. This layer begins to melt at a temperature of about 560.degree. C. and removes an oxide film from the surface of the aluminum material without undergoing any chemical reaction with aluminum.
It has, however, been considered desirable to develop a flux having a lower melting point to enable a lower brazing temperature to reduce the amount of heat required and facilitate the brazing operation. Moreover, K.sub.2 AlF.sub.5 is not suitable as a flux for brazing an aluminum material containing magnesium, since its chemical reaction with magnesium renders brazing difficult.